浅埋下穿公路隧道管棚预支护机理及监测分析

针对软岩公路隧道施工中的超前管棚施作问题,采用双参数地基梁模型,分析了大断面浅埋软岩隧道超前管棚的受力机制,对比分析了工程中常用的Φ76和Φ108的2种超前管棚的支护效果,研究结果表明:①管棚的受力和变形主要集中在掌子面前4 m范围内,管棚的梁支撑作用效果明显,采用Φ108管棚比采用Φ76管棚的最大挠度减小约36%。②超前管棚将上部荷载传递到已开挖隧道初支结构及掌子面前方围岩,起到梁支撑的作用,从而提高掌子面围岩的稳定性,而采用Φ108管棚能承担更多的上部围岩压力,更好地控制围岩位移。应用上述管棚弹性地基梁模型,成功指导了云南大永高速公路大断面软岩公路隧道下穿既有公路工程,将Φ76管棚方案调整为Φ108管棚方案后,最大拱顶地表沉降值减少了38%,保障了整个下穿施工过程的安全顺利。

Analysis of Field Monitoring and Mechanism of Advanced Support of Pipe-roof for Shallow-buried Highway Tunnel to Underpass Highway

More attentions are paid on the problems of pipe-roof for construction of highway tunnels,a double-parameter elastic foundation beam model of pipe-roof is applied in the shallow buried weak tunnel with supper-large section.The mechanic behavior of the pipe-roof is analyzed.The supporting effects of two commonly used types of pipe-roofs(Φ76 and Φ108)are compared and analyzed.The research shows that:(1)The tunnel's deformation and the rock mass's stress variation mainly appear in the section no more than 4m ahead of the working face.The pipe-roof plays a role of support beam and bear the most of the upper load during the tunnel's excavation.The maximum deflection of theΦ108 pipe-roof is reduced approximately 36%,comparing with the Φ76 pipe-roof.(2)The pipe-roof plays a role of supporting beam to improve the stabilization of the working face.It can transfer the upper load to the excavated tunnel and the un-excavated section.The using of Φ108 pipe-roof has more advantages on the pressure loading and the surrounding rock mass's displacement.The achievements are successfully applied in the shallow buried tunnel's construction.The tunnel's section is large,and the surrounding rock mass is very weak,and an existing highway project stands nearly.By changing the using of Φ76 pipe-roof to Φ108 pipe-roof,the maximum surface settlement value has decreased by 38%.The engineering application shows that the tunnel's construction is safe and the achievements are reasonable.